Thanks for writing to the forum!
The smell of ammonia in the urine comes from "urea". Bacteria that contaminate the urine will convert chemicals in the urine into smelling chemicals that are responsible for the distinctive smell, such as ammonia. You can give his urine sample for testing. With a kidney stone chances of infection are high.
Some foods like proteins cause the excretion of nitrogen compounds (ammonia and urea). Hence these foods can be reduced in diet.
Hope these tips help. If symptoms persist consult an urologist. Please let me know if there is any thing else and do keep me posted. Take care!
Thanks for the info. We had him started on an antibiotic yesterday. At his age and health, your input is greatly appreciated.